1. Field of the Invention
This invention relates to a high-frequency power synthesizing apparatus and, more particularly, to a high-frequency power synthesizing apparatus based on a power synthesizing method.
2. Description of the Prior Art
High-frequency power synthesizing apparatuses in general make use of microwave electronic tubes and, therefore, cannot be reduced in size, and they experience other problems in operation, such as heat generation. For this reason, development of high-frequency power synthesizing apparatuses using semiconductor devices is now being promoted.
In a high-frequency power synthesizing apparatus using semiconductor devices, especially when this kind of apparatus is of a high-output type, a single amplifier cannot sustain an operation necessary to generate the required power. To cope with this, a type of high-frequency power synthesizing apparatus based on a method of power synthesis has been made public.
A typical circuit module for use in a power synthesizing method is of a 90.degree.-hybrid type.
FIGS. 8 to 10 show a high-frequency power synthesizing apparatus for synthesizing power to applying 90.degree.-hybrid modules. As shown in FIGS. 8 to 10, the high-frequency power synthesizing apparatus is constituted by an excitation unit 1, a power distributing means 50 which is connected to the excitation unit 1 and which comprises power distributors arranged in a plurality of stages, an amplifying means 60 consisting of a plurality of amplifiers 60a to 60h which are supplied with outputs from final-stage power distributors 50A to 50D which constitute part of the power distributing means 50, and which amplify them to predetermined levels, and a power synthesizing means 70 which comprises a plurality of synthesizers 70A to 70D which are supplied with outputs from the amplifying means 60, and a synthesizer which is disposed at a stage following those of the synthesizers 70A to 70D. The output from this high-frequency power synthesizing apparatus is supplied to an external load 7 via an output terminal B, an isolator 5, and a directional coupler 6.
All of the power distributors 50A to 50D and the power synthesizers 70A to 70D are of 90.degree.-hybrid modules. In the operation of distributing, amplifying and synthesizing power by the thus-constructed high-frequency power synthesizing apparatus, the total reflection coefficient due to phase shifts between reflection waves as seen from input terminals A and B is greatly reduced.
However, with respect to each of the 90.degree.-hybrid modules, the distance S between the terminals is not less than 1/4 wavelength of the operating frequency, as shown in FIG. 8, and the width W of the 90.degree.-hybrid module cannot be reduced to be equal to or below 1/4 wavelength.
For this reason, pairs of power distributors 50A and 50B, 50C and 50D on the input side of the amplifying means 60 and pairs of power synthesizers 70A and 70B, 70C and 70D on the output side of the amplifying means 60 are necessarily arranged in such a manner that they face each other in a surface contacting manner, as shown in FIG. 10.
In the high-frequency power synthesizing apparatus, it is necessary to prevent excessive heating by using a suitable heat sinking means in order to limit internal heating. However, the above arrangement cannot ensure sufficient heat sinking effects, and this sometimes results in malfunctions of the apparatus.
Moreover, the distance between the terminals of each of the amplifiers 60a to 60h must be increased if the outputs from the multiplicity of amplifiers 60a to 60h is synthesized at a comparatively low frequency, thereby necessitating relatively long cables for connection to the amplifiers 60a to 60h. For this reason, too, the size of the apparatus is inevitably increased and, at the same time, troublesome tasks of wiring and adjusting the wiring are involved.
The power distributing means 50 and the power synthesizing means 70 used in the above-described power synthesizing method are used to obtain a high level of high-frequency output, and, specifically, the power synthesizing means 70 is required to operate smoothly at a high level of power. Also, for effective power synthesis, there are strict conditions in respect of of characteristics dispersion imposed upon the amplifiers 60a to 60h, such as the equality of amplitude of the outputs from these amplifiers and the predetermined relationship between the phases thereof.
However, the tolerance within which dispersion of the amplitude and phase characteristics of each may be amplified relative to the others is very narrow. Therefore, to substantially equalize the amplitude and phase characteristics of the amplifiers over the entire operating range from low power to high power, it is necessary to consider an abnormality check and changes in temperature when the gain of each amplifier is adjusted or when power is synthesized. This is time-consuming and troublesome.
If such adjustment is omitted, there is a possibility of control failure occurring due to secular changes, resulting in damage of the power synthesizing apparatus.
It is also necessary to perform overall adjustment in order to eliminate bad influence due to errors in the power distributing means 50 and the power synthesizing means 70 after assembly of the high-frequency power synthesizing apparatus. This adjustment is performed in such a manner that the level and relative phase difference of the output from each of the amplifiers 60a to 60h are set to predetermined values.
In the process of undertaking this adjustment, the output from each of the amplifiers 60a to 60h is adjusted after a corresponding one of the connection cables 80 which connect the power synthesizing means 70 and amplifiers 60a to 60h has been disconnected and after the amplifier has been connected to a measuring tool. Thereafter the connection cable 80 is connected again, thus completing the apparatus. One of the reasons for employing this process is that it is difficult to reproduce by any other method proper dispersion of the amplifiers 60a to 60h (temperature distribution, etc.) and dispersion of the cables 80 which must be observed after they have been mounted. In this adjustment, the operation of changing the connection of each cable 80 must be performed repeatedly, resulting in an increase in the number of assembly steps and in the possibility of cable connectors being damaged.